Widespread sensor network applications such as health monitoring using wireless sensors [1]} and the Internet of things (IoT)[2]}, as well as applications like stock market trading and vehicular networks [3]}, require sending several status updates to their designated recipients (called monitors). Outdated information in the monitoring facility may lead to undesired situations. As a result, having the data at the monitor as fresh as possible is crucial.
In order to quantify the freshness of the received status update, the age of information (AoI) metric was introduced in [4]}. For an update received by the monitor, AoI is defined as the time elapsed since the generation of the update. AoI captures the timeliness of status updates, which is different from other standard communication metrics like delay and throughput. It is affected by the inter-arrival time of updates and the delay that is caused by queuing during update processing and transmission.
